How to Apply Polyurethane

Getting a smooth, smudge-free finish with oil-based polyurethane is within your reach by following the steps in this article. The oil-based polyurethane varnish enhances the natural beauty and texture of the wood. Our 8-step approach shows you how to apply the varnish successfully. A good quality natural bristle brush, a reasonably dust-free and well-ventilated space, and a little patience are all you need.

Finish off your woodworking project or furniture repair job with an oil-based polyurethane varnish to bring out the natural beauty and texture of the wood. Learn how to prepare your wood surface and successfully apply a perfect finish with these detailed steps.

Tools needed

  • sanding block
  • shop vacuum

Required materials

  • Automotive polishing compound
  • Automotive friction compound
  • lint-free cloth
  • Mineral spirits
  • Oil-based polyurethane
  • sandpaper
  • tack cloth
  • wet/dry sandpaper

We use an oil-based polyurethane finish, although you can also use water-based urethane finishes to great effect. But the color and depth you get is no match for oil-based urethanes. If you choose a water-based product, the process for obtaining a smooth finish is basically the same. Just be sure to use a dust-proof cloth that is suitable for water-based finishes, such as gauze moistened with denatured alcohol.

Step 1: sand the surface

  • Sand your project with increasingly fine sandpaper grits.

Note: Paper with a higher grain number removes the deeper scratches left by paper with a lower grain number.
Pro Tip: Most projects need an initial sanding with a medium sandpaper (100 grit) followed by a fine sandpaper (150 grit) and then superfine sandpaper with 220 grit.

Step 2: remove the dust

  • Once the wood is free of stains, remove the dust.

Pro Tip: Use a vacuum cleaner with a soft brush, followed by a clean, lint-free cloth moistened with mineral spirits.

  • As the last dust cleaning step, wipe the surface with an adhesive cloth.

Step 3: seal the surface

  • Thin oil-based polyurethane with two parts polyurethane and one part mineral spirits.

Pro Tip: Pour the products into a glass jar and gently stir the mixture with a stirring rod.

  • Brush the sealer with a natural bristle brush in long, even strokes. Make sure you catch all the runs.

Note: Some stains seal on their own. See the can for this information. If the stain is self-sealing, you can skip this step.
Pro tip: never shake a polyurethane can! You will introduce air bubbles into the mixture that will end up as bumps on the finished surface.
Pro Tip: Use a good quality natural bristle brush to apply oil-based polyurethane. Synthetic Blast Tip Brushes (with each strand divided into multiple strands at the tip) can introduce air bubbles into the finish.

  • Load your brush by dipping it about 1 inch into the mixture and brush the wood with long, even strokes from edge to edge.
  • Maintain an overlapping wet edge with each pass until the surface is completely covered.
  • Collect all the drops with your brush and apply them on the surface.

Step 4: Apply the first layer of polyurethane

  • Within 24 hours of applying topcoat, apply topcoat directly from can.

Pro Tip: Avoid rubbing the brush over the rim of the can, as this can cause air bubbles.

  • Spread the varnish over the entire surface in long, even strokes.

Pro tip: don't use too much or it's likely to leak; use just enough to get a nice even coat with no dry spots. Once the surface is covered, rebrush with the grain, end to end.

  • Overlap your strokes to get an even layer.
  • Capture all drops, especially at the lower edges.

Step 5: remove the bumps

When the surface is completely dry to the touch (at least 12 hours), cut off any drops with a razor blade.
Pro Tip: Make sure you don't cut below the surrounding surface.

Step 6: Wet Sand the First Coat

  • After the primer has dried for 24 hours, remove small spots by wet sanding with 400-grit sandpaper mounted to a sandpaper block.
  • Dip the sandpaper in the water and use circular motions to remove any stains and dust.

Pro Tip: Use enough water to lubricate the sandpaper so you don't burn the delicate finish. Sand just enough to remove the stain.

  • When the surface is smooth, wipe it with a damp cloth and dry it with a clean, dust-free cloth.

Apply the second coat

  • 24-48 hours after applying the first coat, apply the second and last coat using the same procedure as the first coat.

Step 7: Repeat steps 5 and 6 if necessary

  • Once the second coat is dry, scrape off any bumps (per Step 5) and sand the surface with damp sandpaper (per Step 6).

Note: Follow these steps only if absolutely necessary. If you have to sand the second coat, you will need to polish the surface.

Step 8: Buff the surface if you sand the second coat

  • Wait at least 48 hours and then buff the finish with an auto scrubbing compound.
  • Dampen a clean cotton cloth with water and apply an automotive friction compound to the surface in a circular motion.

Note: The compound has a fine abrasive that removes any scratches left by the 400-grit sandpaper and restores the gloss to the polyurethane finish.

  • After scrubbing, allow the surface to dry and buff the finish with a clean, dry cloth.

Pro Tip: If the finish is still a bit hazy, apply more car polishing compounds using the same method. Allow to dry and then buff the surface.
Pro Tip: For an even higher shine, apply a polishing compound as a final step.

We hope you enjoy watching this video about Tips to Apply Polyurethane Like a Pro

Source: Live Free

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